When do I have to use hours and o'clock in a programming document?
For example, I have to show that the program runs at 23:45, should I use o'clock or hours?

I used hours but my manager says that it's not right and I should use o'clock?

Which is the right one?


23:45 is all that is needed here. No disambiguating label like hours is required unless there is an obvious risk that the time of day 23:45 could be confused with something else, such as the duration of an astronomical event.

You would only use o'clock when referring to a precise hour and using the 12-hour clock, e.g. "It is now 11 o'clock". It would not be normal in most (or possibly any) varieties of English to say "It's eleven forty-five o'clock" or — more outlandish still — "It's twenty-three forty-five o'clock".

The label hours is usually used when specifying the time in a formal context like radio broadcasting, especially when the 24-hour clock is being used — for instance, when a newsreader says "It's 23 hours. Here is the news", or when it is necessary to be precise in a military or scientific context ("The evacuation training starts at 23:45 hours").

  • To answer your now-deleted supplementary question, "Would it make sense if I write 23:45 hours in the programming terminology as this time refers to the starting time of a program?": you can do what you describe, but as I wrote in my answer it is not necessary unless there is a risk of mistaking time of day for duration. – Erik Kowal Mar 2 '15 at 9:28

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